The present invention relates to interpolymers (including copolymers) of ethylene with one or more C8-20 vinyl aromatic monomers, which polymers have a highly alternating structure. That is the polymer has to the extent possible a structure of alternating ethylene and the vinyl aromatic monomers.
Polymers of one or more alpha olefins are generally incompatible with polymers of one or more C8-20 vinyl aromatic monomers. As a result, it is difficult to blend or even laminate, for example polystyrene and polyethylene. There have been a number of attempts to prepare copolymers of, for example styrene and ethylene. Such polymers could lead to two different developments. The copolymer might have the properties sought after in the blend or the copolymer may be a suitable compatibilizer so that the blend could be prepared.
U.S. Pat. No. 6,066,709 issued May 23, 2000 assigned to Denki Kagaku Kogyo Kabushiki Kaisha discloses an ethylene styrene copolymer having from 1 to 55 mole % of an isotactic ES structure having a head to tail bond structure (e.g. ESSE). The polymers of the present invention have 13C NMR peaks at 25.7 indicating an atactic structure rather than isotactic structure.
U.S. Pat. No. 6,191,245 issued Feb. 20, 2001 to Campbell et al., assigned to the Dow Chemical Company teaches copolymers of one or more alpha olefins and one or more vinyl aromatic monomers which are substantially random (Col. 6 lines 45-48). The polymers of the present invention have a significantly higher degree of alternating structure than that predicted by Bernoullian statistical modeling. The ratio of the amount of triads having the sequence vinyl aromatic monomer, ethylene, vinyl aromatic monomer divided by the calculated amount of triads having the same sequence as determined by Bernoullian statistical modeling is from greater than 1.5 to 9.5.
U.S. Pat. No. 5,703,187 issued Dec. 30, 1997, assigned to the Dow Chemical Company teaches pseudo random co-polymers of styrene and ethylene. The specification teaches a particular distinguishing feature of pseudo random copolymers is that all the phenyl groups substituted on the polymer backbone are separated by 2 or more methylene units. No styrene was inserted in a head to tail manner. The polymers of the Dow patent do not have the high degree of alternating nature of the polymers of the present invention. Additionally, the process for preparing such polymers uses a catalyst distinct from that disclosed in the reference.
U.S. Pat. No. 6,191,245 B1 filed by the Dow Chemical Company claims a substantially random structure of an ethylene styrene copolymer with a head to tail insertion. The reference teaches that the styrene in the styrene ethylene tetrad (ESSE) is inserted exclusively in the head to tail manner. The patent teaches away from ES in an alternating structure.
There are a number of Idemitsu Kosan Co. Ltd. patents which teach polymers comprising blocks of syndiotactic polystyrene (the phenyl rings are alternating on opposite sides of the back bone) and the olefin is incorporated in repeating units (e.g. olefin blocks). The patent teaches blocks of syndiotactic polystyrene and does not suggest ES in an alternating structure. Additionally, the process for preparing the block copolymers does not use the catalyst system contemplated by the present invention.
U.S. Pat. No. 5,043,408 issued Aug. 27, 1991 teaches an ethylene styrene copolymer having alternating ES units. However, the polymer has an isotactic diad of the ES repeating units of not less than 0.55 (i.e. greater than 0.55). The polymers of the present invention are essentially atactic ES having head to tail and tail to tail SS microstructure.
U.S. Pat. No. 6,235,855 issued May 22, 2001 teaches an ES polymer having isotactic styrene blocks. The alternating polymer of the present invention contains not more than two styrene monomers in a row and consequently does not contain polystyrene blocks.
The present invention seeks to provide a highly alternating polymer comprising ethylene and one or more vinyl aromatic monomers in which, in the triad sequence of vinyl aromatic monomer and ethylene as determined by 13C NMR, the triads have the sequence vinyl aromatic monomer, ethylene, vinyl aromatic monomer and the ratio of the amount of triads having the sequence vinyl aromatic monomer, ethylene, vinyl aromatic monomer divided by the calculated amount of triads having the same sequence, as determined by Bernoullian statistical modeling, is from greater than 1.5 to 9.5.
The present invention provides a highly alternating interpolymer consisting of from 20 to 70 weight % of ethylene and from 80 to 30 weight % a C8-20 vinyl aromatic monomer wherein:
(i) in the triad sequence of vinyl aromatic monomer and ethylene as determined by 13C NMR, the triads have the sequence vinyl aromatic monomer, ethylene, vinyl aromatic monomer and the ratio of the amount of triads having the sequence vinyl aromatic monomer, ethylene, vinyl aromatic monomer divided by the calculated amount of triads having the same sequence as determined by Bernoullian statistical modeling is from greater than 1.5 to 9.5;
(ii) said polymer has ES repeating units essentially in an atactic configuration;
(iii) the maximum number of sequential vinyl aromatic monomer units in sequence does not exceed 2; and
(iv) said polymer containing ES repeating unit, having head to tail and tail to tail SS microstructure present.
The present invention further provides a process for preparing the above highly alternating interpolymer, comprising contacting a monomer mixture comprising from 70 to 30 weight % of a C8-20 vinyl aromatic monomer and from 30 to 70 weight % of ethylene with a catalyst comprising a phosphinimine compound of the formula:
Lxe2x80x2((R1)3Pxe2x95x90N)xe2x80x94Mxe2x80x94L2 
wherein each R1 is independently selected from the group consisting of C3-6 alkyl radicals, M is selected from the group consisting of Ti, Zr and Hf, and each L is independently selected from the group consisting of a halogen atom, a hydrogen atom, a C1-10 alkyl radical, a C1-10 alkoxide radical, and a C6-10 aryl oxide radical, Lxe2x80x2 is an anionic ligand having up to 50 C, H, O, N, Si and P atoms and at least one activator selected from the group consisting of:
(i) a mixture comprising complex aluminum compound of the formula R22AlO(R2AlO)mAlR22 wherein each R2 is independently selected from the group consisting of C1-20 hydrocarbyl radicals and m is from 3 to 50, and a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1; and
(ii) ionic activators selected from the group consisting of:
(A) compounds of the formula [R3]+[B(R4)4]xe2x88x92 wherein B is a boron atom, R3 is a cyclic C5-7 aromatic cation or a triphenyl methyl cation and each R4 is independently selected from the group consisting of phenyl radicals which are unsubstituted or substituted with from 3 to 5 substituents selected from the group consisting of a fluorine atom, a C1-4 alkyl or alkoxy radical which is unsubstituted or substituted by a fluorine atom; and a silyl radical of the formula xe2x80x94Sixe2x80x94(R5)3; wherein each R5 is independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical; and
(B) compounds of the formula [(R8)tZH]+[B(R4)4]xe2x88x92 wherein B is a boron atom, H is a hydrogen atom, Z is a nitrogen atom or phosphorus atom, t is 2 or 3 and R8 is selected from the group consisting of C1-8 alkyl radicals, a phenyl radical which is unsubstituted or substituted by up to three C1-4 alkyl radicals, or one R8 taken together with the nitrogen atom may form an anilinium radical and R4 is as defined above; and
(C) compounds of the formula B(R4)3 wherein R4 is as defined above;
(iii) mixtures of (i) and (ii);
in an inert hydrocarbyl medium at a temperature from 20xc2x0 C. to 150xc2x0 C. and a pressure from 15 psi (103 KPa) to 600 psi (4,137 KPa).